Conventionally, to detect the operation of a three-phase brushless motor, a detector may be disposed on the magnetic pole of its rotor or on the rotor shaft. The detector has to be attached precisely on the rotor shaft to let the motor operate normally. Also, a space in the motor needs to reserved to mount the detector and its electric cords. The volume size and the operation cost of the foregoing motor may be increased, and the additional electric devices may dissipate more power. Recently a sensorless motor control method has been proposed, which needs a corresponding driving circuit to detect position of the magnetic pole in the motor indirectly and to operate the motor. However, the sensorless control method is used in the prior art to drive motors, without including the function of energy recovery to recycle possible electric energies. Even though the regenerative braking method has been proposed to recycle energy in motors, the energy-recovery efficiency therein is still not satisfied.
Therefore, it is in need of an apparatus and method for driving a sensorless motor of energy recovery ability, which can perform the energy-recovery operation automatically with an improved efficiency. And thereby, the volume size of the motor can be diminished with improved operable power.